...then goes into the women's bathroom to masturbate...
Has this ever happened? Ever?
And as KeithInc. said, how could you tell a person's motivation? And what difference would it make?
Claiming that ALL transmen are poor pitiful women "trying to escape sexualization" plays up the cliché of women as weak and helpless victims of male sexuality, damsels in distress unable to cope with the male gaze. It's a load of bullshit!
Transphobes seem to carry a lot of emotional baggage around sexuality. They would do better to leave trans folks alone and get themselves into therapy.